I'm currently working on a small project for school where I shall compare distorsion in Class A and Class A/B amplifiers.

I have decided to use a John Linsley Hood construction for my class-A amp and am thinking of building the Trimodal Amplifier by Douglas Self for comparison. I have the circuit in print in the book "Audio Power Amplifier Design Handbook" but would prefer to have it in digital form. I have searched for it on the net, but to no avail. Does anyone know where I can find it?

Also if anyone have Spice3-models of it and are willing to share it I'd be very happy.

I'm also searching for a good program to draw circuit diagrams, currently I use xfig but it is not very convenient to work with. My computer is an iBook with Mac OS X, that means I can run all BSD/Linux programs but not old macintosh applications. Since I only have low-level education and are rather young, I'm not qualified to a student-license, so the application can't be very expensive, free would be preferable.

Here you will find "DesignWorks Lite". It is one of the best and easy to use schematic drawing programs I’ve ever seen. Price is $39,95. But to my opinion it is definitely worth the money. Anyway you have a free trail of 30 days:

I am wondering why you want to build two different amplifier circuits to compare class A and class B. Won't it be difficult to know which distortion differences are due to the class and which are due to the design? Have you considered building just a single circuit and changing its output bias current to change it from class B to class A?

I am wondering why you want to build two different amplifier circuits to compare class A and class B. Won't it be difficult to know which distortion differences are due to the class and which are due to the design? Have you considered building just a single circuit and changing its output bias current to change it from class B to class A?

Good point, but isn't Douglas Self's Trimodal Amplifier switchable between class A and class B (and class AB). So you only need to build this one.

Originally posted by Pjotr
The guys at Capilano are real Mac heads and are writing professional Mac software for some 20 years now.

I did some work for one of the guys (and met the son) who started this (probaly one of the guys still) and they indeed are top notch -- i owned, and never used, a very early version of this.

I use VectorWorks (general CAD) for doing my schematics, but it doesn't qualify as cheap. There are a couple budget CAD programs, the one i can actually put my fingers on is Cadintosh by the same guys who do GraphicConverter. A Carbon version is available.

It would also be a good idea to scan thru Made4Mac and download.com. A good PCB layout program can be had from Osmond -- a carbon version of that is also available.

In the late 80ties I did an extensive search for CAD software for the Mac. In those days the people at Capilano were the only ones that understood that hardware people are working completely different than software people. So they came up with a piece of software (DesignWorks) that was easy to use by hardware people and relatively bug-free. Later on they came with a nice Mac version of ABEL, a PLD design package originally developed by DATA IO. In those days there was only some crude DOS software, programmed to the “bare steel”, or there was software for Unix mainframes costing tons.

I still use a 68k version (V3.5) running on Basilisk for quick setting up prototyping schematics. Once you have made your own collection of libs it works pretty fast. I also still use it for schematics that have to go in print. When printed to a .ps file is can be easily imported in AI for touch-up.

IMO their software is still standing out the mass out there when you concern the price, graphics capabilities and ease of use. But it is schematic capture only.

When working on a win-system I would recommend using the already mentioned SpectraSoft software. The schematics capture part is also good and easy to use and it is FREE.

--------------------------------------------------

Nils, are you still there?

Attached the schematic of the tri-modal amp I have found. It is not of my own so I can’t take responsibility for it.